This proposal is directed towards obtaining detailed information on the structural and functional properties of the antigen-specific surface component of some murine and primate T cells which is related to immunoglobulin. We propose that the primary receptor for antigen on T cells resembles serum antibodies and B cell surface immunoglobulins in its combining site but possesses distinct constant regions. The major specific aims of this proposal are as follows: (1) To produce antibodies against combining site determinants of human and murine Igs by immunizing phylogenetically diverse species, e.g., chickens, with (Fab') and VH fragments of pooled Ig, antibodies of restricted heterogeneity and myeloma proteins. Monoclonal hybridoma antibodies will also be produced against these fragments. (2) To use these antibodies to detect Ig-related products of normal and neoplastic T cell subsets; (3) To investigate the capacity of these antisera to inhibit primary antigen-binding by specific T cells and also functional T cell activities; e.g., generation of cytotoxic T cells, antigen-specific proliferation, helper activity and suppressive activity. (4) To characterize the T cell Ig-related material in terms of its physical association with the plasma membrane, and with other membrane components, e.g., MHC-products and Lyt antigens. (5) To characterize the Ig-related molecule(s) serologically by quantitative radioimmunoassay comparisons with fragments of characterized serum Igs. (6) To carry out physiochemical studies, characterization of peptides and primary amino acid microsequence analysis of the biosynthetically-labeled T-cell Ig-like product in order to establish its relationship to serum and B-cell associated Igs. The proposed structural comparisons between Ig-related T cell products of murine and primate (human, cotton-topped marmoset) should allow an estimation of the extent of evolutionary conservation of these receptor molecules.